In healthy individuals, tear fluid (that is “lacrimal” fluid) is normally supplied continuously to their eyes from lacrimal glands, each being located in a lateral and superior relation to the respective eye. Upper lacrimal ducts feed the fluid from each gland to a respective conjunctival sac, in which the relevant eyeball is partially encased. The lacrimal fluid subsequently washes the sclera and other conjunctival components of the eye, as well as its cornea.
Under such healthy conditions, excess lacrimal fluid that cannot be retained by each eye and conjunctiva tends to be drained (see FIG. 1 of the drawings accompanying this specification) from the inner-canthus (1) (at the corner of the eye) to the nasal passages (7a,b), in particular to the inferior nasal meatus (7b). The nasal passages are separated by the nasal septum (9).
After any excess fluid has drained from the inner-canthus (1), it passes through a network of passages commencing with the puncta, which are seen as small papillae (2, 3) adjacent to the inner-canthus (1). From here, the lacrimal fluid is subsequently collected in the lacrimal sac (6), which is connected to the puncta via the canaliculi (4, 5). The lacrimal fluid is thereafter drained through the nasolacrimal duct (8) into the interior meatus (7b) of the nose.
Sometimes, if an unwanted closure of the passageways of the system occurs, for example by way of a blockage of any one or more of its sub-components, excess lacrimal fluid can no longer be disposed of in the usual way. Such a blockage can result from, inter alia, congenital anomalies, accidents, inflammation, advancing age, and so forth, and tends to cause the eye to continuously brim over with tears, with concomitant discomfort to the individual.
More seriously, if the blocked tears stagnate, they can become infected, which can then lead to inflammatory irritation of the mucous membranes of the affected passage. In turn this can result in proliferation of local epithelium, as well as hyperaemia, and even a purulent exudation into the conjunctiva. Infection caused in this way can ultimately lead to scarring over of the canaliculi (4, 5).
In severe cases, the resultant permanent closure can require a corrective surgical procedure. In some of these cases, only the defective portion of the lacrimal drainage system needs to be reconstructed. Thus, if the sole blockage occurs in, for example, the nasolacrimal duct the remaining lacrimal sac cavity can be joined directly with the mucosa of the nasal fossa, a procedure known as a dacryocystorhinostomy (DCR). This is typically achieved by removing tissue, including the intervening segment of nasal bone and periosteum, so that the drainage of tear liquid into the nose can be more or less restored.
In other cases, however, it may not be possible to re-connect or repair any part of the natural tear drainage system. Occasionally, the new connection after a DCR operation may be patent but fail to drain tears. In these situation the insertion of a replacement mechanical device (for example a bypass tube) is then required.
Conventionally, the bypass tube utilised in tear-duct surgery has been a small tube constructed of Pyrex™ glass, stiff plastic or some other relatively rigid material. However, usually it is Pyrex™-type glass that has been preferred, since this can neither be destroyed, nor corroded or otherwise affected by a patient's bodily fluids.
These tubes of Pyrex™ glass are generally known by surgeons as “Lester Jones” tubes, being named after their designer, Mr Lester T Jones, and are sometimes simply referred to as “Jones” tubes. Very similar devices go by the alternative trade names, such as “Callaghan Cox”, “Gladstone Putterman”, “Baylis”, and “Naugle” tubes. As shown in FIG. 1B, these bypass tubes 10 have an external flange 11 that rests at the medial canthus and a length to accord with the patient's anatomy such that, after insertion into the inner corner of the eye, and then down the surgically created passage to the nose, they allow drainage of the excess lacrimal fluid internally into the nose.
Such operations to place bypass tubes have to date seldom been entirely successful, because at least the following two particular difficulties have typically been experienced.
Firstly, due to the lack of a firm attachment between the tube and the patient's tissues, as the tissues heal around the lower end portion of the inserted replacement tube, the latter is gradually rejected from the bone and flesh of the patient. And secondly, the internal opening of the tube may become obstructed either by the patient's flesh tending to heal over this opening if the tube is too short, or through impacting the midline nasal septum if it is too long.
Newer versions of improved Jones tubes have recently been developed, such as those constructed of frosted glass and those having collapsible flanges (see the present inventor's co-pending UK Patent Application no. 0619305.6) to try to overcome these difficulties. Even so, careful selection of the appropriate size of tube for the individual patient's anatomy is essential.
Each tube has a number of variables and each must be selected to be correct for the individual patient. For example, length of tube, external flange diameter and, where used, the location of the internal flange must all be selected.
Whereas the external flange diameter is usually either 3.5 mm or 4 mm, with the choice being at the surgeon's preference or guided by the visible external anatomy, in practice the area that presents a problem is the choice of the tube's length. What is ideally needed to be known is the length of tube that leaves the tip of the tube protruding the optimally desired distance beyond the outer (lateral) nasal wall and into the nasal cavity, whilst remaining clear of the midline septum. Such a proud projection of tubing helps prevent the tube from being blocked after its permanent insertion.
At present this selection is made by educated guesswork (most patients require a tube from only a limited range of lengths) or by using a dipstick 12 (see FIG. 2) passed down the track being formed to take the tube. The dipstick 12 touches the midline nasal septum 9, so being prevented from further insertion. The distance from midline septum to where the head of the bypass tube is expected to lie is then read off the externally visible portion of the dipstick. A sleeve slid down the dipstick which rests on the medial canthus may be used to assist the estimation of this distance. An estimated length of around between 1-3 mm is deducted by the surgeon from this maximum length of dipstick insertion to provide a figure for the size of bypass tube required so as not to impact the midline nasal septum.
When the decision of required length is approached using the dipstick method, at least four main limitations are evident.
Firstly, the dipstick method determines the distance of the tip of the tube from the midline septum but, given that the space inside the nose is very different between individual patients, this provides no real accuracy regarding how far it is beyond the lateral wall. Indeed, as shown in FIGS. 3a and b, in a very tight nasal space 7d the tube might barely 14c enter the nose using this method, whilst in a very wide nasal space 7c the length 14b of tube protruding into the nose may be much greater than needed (14a).
Secondly, due to the flexibility and elasticity of the tissues in the medial canthal region where the external flange of the bypass tube will rest, the estimation of the total distance from the nasal septum to this point is inherently inaccurate. An incorrect length of bypass tube may therefore be selected.
Thirdly, a dipstick is merely a metal stick with a scale on its length that is held in the track created. The track angle and/or direction may not be exactly the one that the tube will eventually lie on once it has been placed in situ, thus the length calculated by the dipstick method has another degree of inaccuracy.
Fourthly, the tip of the dipstick must contact the nasal septum and in doing so is liable to cause some trauma to the mucosa surface.
When considering the question of whether it matters that the length is difficult to calculate accurately using this technique, one might wonder why surgeons do not simply try out different lengths until the right one is found. In practice, before the present invention, this is precisely the method to which most surgeons had to resort. They selected the best guess length possible, tried it in situ, looked inside the nose with an endoscope and either left it if it was correct or replaced it with a longer or shorter one according to how it looked inside the nose.
For most patients, two or three or even more bypass tubes might be used before the correct size is found. The tubes that have been placed in situ during this method that have been found to be of the incorrect size and thus removed could not be re-used in other patients even if cleaned and re-sterilised. Hence, the actual total cost for bypass tubes used is usually higher than for the individual tube that is left in the patient at the end of the operation. Whilst this in itself may not be a very significant extra expense when using relatively cheap standard tubes, the increasing use of newer frosted or collapsibly flanged tubes is made more expensive.
Thus, it is becoming more and more cost-effective to ensure that the tube length selection is right first time.
One aim of the present invention is to provide a very accurate and simple system for ensuring that the initial selection of length for the bypass tube is correct.